Refactored CSS input and dependency parsing

Hopefully a step in the right direction to correctly
support scss. Import handling is quite tricky. The watchdog
should now work correctly for
Preparation for a full featured CSS Parser. Merge features
from sprite generator and generic css/scss handling. This
will enable new and advanced options for the css optimizer.
Merge branch 'refactor' of https://github.com/mgreter/webmerge into refactor
Adds minor fix to suppress warning message